손익분기점

#include <iostream>
using namespace std;

int main()
{
	int price[3];
	
	for (int i = 0; i < 3; i++)
		cin >> price[i];

	if ((price[2] - price[1]) <= 0)
		cout << -1 << '\n';
	else
		cout << (price[0] / (price[2] - price[1])) + 1 << '\n';

	return 0;
}